Dave, I forgot to mention in the last post about the floor.
Of all the pics I've seen of either the M3 75mm GMC or the T19, they all have the sunken floor area for the mount. That pic above is the first and only one I've seen that appears to
not have the rear floor storage lockers installed... yet. It could be a pic of one in the process of being built/modified.
Another interesting feature is in the second picture. If you look closely at the right hand wall, you'll notice that it is sloped with two tie-downs.
I wonder if that wall is another storage locker and the tie-downs are handles... ??? Or maybe it's just an optical illusion?